Prevalence data indicate that military service men and women returning from Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) suffer high rates of PTSD and substance use disorders. With these numbers expected to rise, the co-occurrence of these disorders presents added challenges to the Veterans Affairs treatment delivery system, presently in need of effective integrated treatments. This RO1 proposal is a direct response to NIDA RFA DA-10-001 Substance use and abuse among U.S. military personnel, Veterans and their families. The overarching goal of the this application is to evaluate an integrated cognitive behavioral therapy (I-CBT) for co-occurring PTSD and substance use disorders among OEF/OIF Veterans. I-CBT has been found efficacious in community samples of men and women with this comorbidity, but needs testing for its application to Veterans Affairs (VA) patient samples and settings. To enhance potential translation to VA clinical settings, the intervention has been adapted for delivery in combined individual and group therapy formats. Within the framework of the NIDA stage model of behavioral therapy development, we propose to execute three specific aims within this Stage I research: 1) To evaluate the feasibility of I-CBT with a sample of 16 patients with co-occurring PTSD and substance use disorders, recruited from VA PTSD and substance abuse treatment program (SATP) clinics; and assessed on PTSD and substance use severity at baseline, 3- and 6-month follow-up (Phase I); 2) To make modifications and improvements to the I-CBT based on feasibility study outcomes and qualitative study (Phase II); and 3) To conduct a randomized controlled pilot trial (n=64) comparing I-CBT plus standard care (n=32) versus standard care only (n=32) on measures of PTSD and substance use severity at baseline, 3-month and 6-month follow-up (Phase III). Although there have been two other behavioral therapies for co-occurring PTSD and substance use developed and tested, these treatments have not been found effective versus comparison conditions, have moderate to poor retention rates, have been studied with female civilians only, and have not been integrated within existing treatment services. The present proposal builds upon a series of successfully completed studies by the PI, implementing a cognitive behavioral therapy (CBT) for co-occurring PTSD and substance use disorders in community clinics. The research team is uniquely experienced and well-positioned to execute the research as proposed. It consists of investigators from Dartmouth, the National VA Center for PTSD, Brown University, and the Providence VA Medical Center. The findings from this research have the potential for immediate and broad impact by providing an effective and readily translated behavioral therapy option for OEF/OIF Veterans with co- occurring substance use and posttraumatic stress disorders.